1. Field of the Invention:
The present invention relates to a method of in situ treatment of a wooden railroad tie for terminating the growth of decay fungi, particularly at the interface between the tie and the rail supporting tie plate.
2. Description of the Related Art:
Wooden railroad ties are made decay resistant by forcing a material such as creosote into the wood cell structure under relatively high pressure. This protects the exterior wood layer but the interior is not penetrated by the creosote and is subject to attack by decay fungi whenever the exterior layer is split, cracked, abraded away or otherwise structurally compromised. Penetration of the treated exterior is common after extended service use as a result of weathering and also as a result of what is known as spike kill and plate cut.
Weathering typically causes weather checking in the form of splits or cracks running in the direction of the wood grain. These cracks provide passages for moisture to travel under the tie plate supporting the rail and into the tie spike holes and checks.
Spike kill in the mechanical enlargement of spike holes caused by cyclical train loadings on the rail, spike and tie plate, the relative movement between these components eventually enlarging the spike hole and exposing untreated tie wood. This relative movement also causes plate cut, which is the wearing or cutting away of the tie at the interface between the tie plate and tie. This action tends to abrade away the treated exterior wood layer and expose the tie interior to the intrusion of moisture and wind borne fungi spores.
Soon after railroad ties are put into service moisture sites become established, particularly in the central portion of the interface between the tie and tie plate. This central portion never seems to dry. As a consequence, the presence of moisture and the temperature elevation brought on by exposure to the sun services as an incubator for the growth of decay fungi. The natural balance of food, moisture and temperature accelerates destruction of the wood cells and exaggerates spike kill and plate cut in a cycle which eventually results in premature failure and costly replacement of the ties.
Some railroad companies have attempted to skirt the decay problem altogether by using specially fabricated ties, such as concrete ties, but this has not proved to be satisfactory because of the economics. Such ties are not inherently resilient and costly measures have to be taken to compensate for this. U.S. Pat. Nos. 4,156,440 and 4,267,085, issued to Katoh et al on May 29, 1979 and May 12, 1981, respectively, disclose the use of concrete ties resting on a ballast roadbed, but requiring injection of a layer of thermoplastic material between the ties and the roadbed to disperse the stresses developed when a train passes over the rails.
Various other prior art attempts to more thoroughly protect wooden ties from fungi attack are discussed in U.S. Pat. No. 1,388,877, issued to Moore on Aug. 30, 1921. He indicates that the fungicide material in wooden ties tends to be leached out by the weather, and that attempts had been made to stop this by applying cementitious solution as an external layer to cement the fungicide in the wood. In practice the cementitious material in crevices of the tie expanded and cracked the tie open, exposing the untreated interior, and the presence of the material also enhanced development of decay because the tie interior was absolutely shut off from any ventilation. Another prior art practice described by Moore was the drilling of holes through the tie to provide passages into which additional fungicide could be injected from time to time. However, this method was apparently not successful because if the tie had already been treated with a cementing solution the wood fibers or pores were filled and could not absorb the fungicide. On the other hand, if the ties had not been treated with a cementing solution, the wood pores were open and the liquid fungicide either drained away or was dried out by the wind and sun. In his patent Moore proposes to better treat the tie with fungicide by drilling a relatively large opening or reservoir along the length of the tie, with additional vertical openings in communication with the central reservoir. The tie is then exteriorly treated with oil or other cementing solution, and the reservoir is filled with liquid fungicide and water. The openings are then sealed off. The process is expensive and time consuming and particularly is not adapted for in situ treatment of ties after a period of service.
U.S. Pat. No. 4,202,494 issued to Rumell on May 13, 1980 teaches the treatment of used railroad ties, but he requires that the tie be removed from its operative position for placement in a mold. There a thin layer of polypropylene is molded onto the exterior surfaces and within any rail or tie plate hardware mounting apertures.
Nothing in the known prior art teaches in situ fungicide treatment of worn or weathered wooden railroad ties which harbor pockets of decay fed by moisture traveling along cracks and splits in the wood grain, and into untreated areas of the tie exposed through spike kill and plate cut. Moore makes plain that previous attempts to douse the affected tie areas with fungicide did not work because it either drained away or was eventually leached out. Thus, at best such fungicide might reach existing decay sites, but was not present long enough to combat future or developing decay.